Method for aromatization of light naphthas



United S tes Pa efl O METHOD FOR AROMATIZATION F 1.1GHT NAPHTHAS Charles Newton Kimberlin, Jr., and William Judson Mattox, Baton Rouge, La., assignors to Esso Research and Engineering Company, a corporation of Delaware Application May 29,1956, Serial No. 587,998

3 Claims. (Cl. 20896) The present invention relates to the reforming of hydrocarbons and particularly to an improved method for the aromatization of light naphtha fractions to produce a highly aromatic high octane product.

Hydroforming is a well known and widely used process for. upgrading hydrocarbon fractions boiling in the motor gasoline or naphtha boiling range to increase their octane numbers and to improve their burning or engine cleanliness characteristics. In hydroforming, the hydrocarbon fraction or naphtha is contacted at elevated temperatures and pressures and in the presence of hydrogen or bydrogen-rich process gas with solid catalytic materials under conditions such that there is no net consumption of hydrogen and ordinarily there is a net production of hydrogen in the process. A variety of reactions occur during hydroforming including dehydrogenation of 'hydroformate which burns clearner or forms less deposits 'when used as the fuel in an internal combustion engine.

Hydroforming isusually applied to a rather wide boiling rangenaphtha, i.e. to one having a boiling range of from about 125 F. to about 400-430" F. It has been known 'that the lower boiling naphthas are not substantially improved by a hydroforming process as ordinarily conducted. The extensive report entitled An Appraisal of Catalytic Reforming in Petroleum Processing for August, 1955 for example, states at page 1174, Optimum reformer utilization is obtained by not using feed stock constituents boiling much below 200 R, which do not contribute greatly to increased octane during reforming, as these merely take up reformer capacity better used for high boiling materials more susceptible to octane upgrading.

,In view. ofthe continuing demand for more and higher "octane number gasolines, however, it is becoming increasingly important to Upgrade these lower boiling frac- 'l'tions.

' It is theobject of this invention to provide the art with an improved method for reforming or upgrading light naphthas. i

It is also the object of this invention to provide a simple and eifective method for reforming light petroleum "naphthas boiling in the range of from about l10-250 F.

preferably from about 150 200 F. to form high octane products rich in aromatic constituents.

These and other objects will appear more clearly from the detail of the specification and claims which follow.

It has now been found that light petroleum naphtha fractions can be converted into high octane number,

aromatic-rich products with good yields byhydroforming them in contact with platinum-containing catalysts at pressures below 125 p.s.i.g. and preferably at pressures of from 50 to 100 p.s.i.g. to an intermediate octane number level of approximately 80 and subjecting the resultant product to solvent extraction, particularly with butyrolactone, to obtain an extract having an octane number of approximately 100 and a rafiinate fraction having substantially the same octane number as the original feed which is thereupon recycled to the hydroforming step. By this particular combination of process steps it is possible to obtain an aromatic-rich product having an octane number of between about 98 and 100 in yields'of about 67% based upon the original feed.

It has of course been proposed to subject a reformate or hydroformate to solvent extraction with recycle of the raffinate to the hydroforming step or with further treatment of the raflinate in a separate reaction zone. However, no one has previously proposed to upgrade the light virgin naphthas in such a way. In view of the fact that these light naphthas constitute a very substantial part of the gasoline pool of the refinery and are not amenable to upgrading by the conventional reforming or hydroforming processes, it has now become essential to devise methods for upgrading these light naphthas to the 95 to 100 research octane number level.

Reference is made to the accompanying drawing which diagrammatically illustrates a flow plan of the process in accordance with the present invention.

In the drawing, light naphtha feed is supplied through inlet line 10 to the hydroformer 11 Where it, in admixture with hydrogen or hydrogen-rich recycle gas supplied through line 12, iscontacted with a platinum-containing catalyst maintained under active hydroforming conditions. It will be understood that the hydroforming reaction may be carried out in fixed, moving bed or fluidized solids type operation, that thehydroformer maycornprise several vessels with reheating means between each and that in moving bed or fluidized solids type systems separate reactor and regenerator vessels may be used.

Hydroformate is removed from hydroformer 11 via line 13, cooled or condensed and passed to gas-liquid separator 14. Normally gaseous materials are taken overhead from separator 14 and passed via lines 15 and 12 back to the hydroformer, excess gas being vented or discharged from the system via tail gas outlet line 16. Suitable scrubbing and heating means may be provided to remove impurities from the recycle gas and to preheat the same to the desired temperature for introduction into hydroformer 11.

Hydroformate is removed from separator 14 and passed via line 17 to solvent extraction Zone 18 which may be provided with plates or packing to improve contact of the hydroformate and solvent. Solvent, such as butyrolactone is supplied to the upper part of solvent extraction zone 18 through line 19 and flows downwardly through the zone, selectively removing aromatics from the hydroformate. The normal paratfin raffinate istaken overhead through line 20 and passed to separator 21 for the removal or separation of small amounts of entrained solvent therefrom. The separated solvent is removed through line 22 for recycling to the extraction zone 18. The solvent-free raflinate is removed via line 23 and passed via line 24 to inlet line 10 for the admixture with fresh feed and recycling therewith to the hydroformer 11. If desired, part of the raffinate may be withdrawn via line 25 for use as a solvent, fuel or the like.

The aromatic-rich extract phase is removed from solvent extraction zone 18 via line 27 and passed to solvent recovery zone 28 wherein solvent is separated from the aromatic extract by distillation, treatment with water and the like. The high octane number motor fuel product is removed from zone 28 through line 29 and .is passedJo product storage or blending. The separated solvent is removed through line 30 and is pumped through line 32 to inlet line 19 to the solvent extraction zone.

The light virgin naphthas that may be treated in accordance with the present invention boil in the range from about 110 to 250 F., preferably in the range of 150 to 200 F. The C fraction boiling below about 150 F. is not upgraded by the process to as great an extent as the C and C hydrocarbons and therefore the C fraction is not a particularly desirable component of the feed. On the other hand the presence of C s in the feed is not particularly harmful so that it may be preferred to include this fraction in the feed if doing so will avoid an additional distillation step in the feed preparation. The fraction boiling above 200 F. up to 225 or 250 F. responds fairly well to the conventional 'hydroforming processes, employing either molybdenum oxide or platinum catalysts at about 200 psig. or higher and may be included in the feed to such processes if desired. On the other hand, this fraction also responds well to the present, low pressure platinum catalyst conversion process so that the method of handling this particular fraction of the virgin naphtha feed will depend upon circumstances, such asavailability of equipment and the volumes of the different boiling range fractions which it is desired to process.

It has been found that in the pressure range from about atmospheric pressure to about 125 p.s.i.g. it is possible with platinum-containing catalysts to upgrade a light virgin naphtha having a mean average boiling point of 169 F. and a research clear octane number of 66 into a hydroformate having a research clear octane number of around 90 and higher in yields of about 75 vol. percent. In contrast thereto, hydroforming of this naphtha at 200 p.s.i.g. with a molybdenum oxide catalyst produces a hydroformate of only about 81 research octane number in yields of about 75 vol. percent or about 85 research octane number in yields of about 68 vol. percent. In further contrast thereto, hydroforming of this light naphtha at 200 p.s.i.g. with platinum-containing catalysts produces a hydroformate of only 85 research octane number at 75 vol. percent yield. Moreover, it was found impossible to increase the research octane number much above about 85 by hydroforming this light naphtha with platinum-containing catalysts at 200 p.s.i.g.

Under these reaction conditions there is a tendency for carbon to form on the catalyst and it therefore becomes necessary to regenerate the catalyst by burning the carbonaceous deposits from the catalyst. Regeneration is preferably effected with diluted air to facilitate control of temperature of regeneration and it is preferred to contact the regenerated or carbon-free catalysts with undiluted air or oxygen-enriched gas at temperatures of 850 :to 1100 F. for from about 1 to 4 hours. The hydro- -forming reaction may be carried out in a fixed-bed, moving bed or fluidized solids type operation, the latter being preferred when reaction conditions are such that frequent regenerations are necessary.

It is also desirable to provide means for subjecting regenerated platinum catalyst, or a portion of it, in continuous operation to reactivation with a halogen or halogen compound such as chlorine or hydrogen chloride. A free halogen such as chlorine is the preferred treating agent for reactivation. Aside from the accumulation of poisons, the deactivation of platinum hydroforming catalysts proceeds by two mechanisms: (1) the loss of chlorine or other halogen that is normally present as a part of the catalyst composition and that contributes substantially to the catalyst actvity and (2) the agglomeration of the platinum metal into relatively large .ormassive I crystals having diameters in excess of about 50 Angstrom units. Treatment of the catalyst with a halogen compound such as hydrogen chloride or the like is effective in, restoringrthe halogen content of the catalyst to the formed by spray-drying an alcoholate alumina hydrosol range of from 800-975 F.

. forming reaction zone.

- separator.

desired level and, to this extent, is efiective in restoring the activity of the deactivated or'partially deactivated catalyst. On the other hand, treatment of the catalyst with an elementary halogen such as chlorine or the like not only restores the catalyst halogen content to the desired level, but also accomplishes the redispersion of the platinum metal by breaking up the large platinum crystallites. This treatment, therefore, is entirely elfective in restoring the activity to the deactivated catalysts whose activity loss was not due to the accumulation of poisons such as arsenic or the like.

Catalysts that may be used for hydroforming the light naphthas in accordance with the present invention are those containing 0.01 to 1.0 wt. percent platinumor 0.1 to 2.0 wt. percent palladium dispersed upon a highly pure alumina support such as is obtained from aluminum alcoholate as per U.S. Patent 2,636,865 or from an alumina hydrosol prepared by hydrolyzing aluminum metal with dilute acetic acid in the presence of very small, catalytic amounts of mercury. A suitable catalyst comprises about 0.1 to 0.6 wt. percent platinum widely dispersed upon alumina in the eta phase derived from aluminum amylate and having a surface area of about 150-220 m. g. A preferred catalyst for fluidized solids operations is one comprising a mixture of a platinum catalyst concentrate consisting essentially of 0.3 to 2.0 wt. percent platinum on alumina micro-spheres prepared in accordance with U.S. Patent 2,656,321 and mixed with suflicient unplatinized alumina to form a catalyst composition containing about 0.01 to 0.2 wt. percent platinum.

The pressure in the reaction zone should be in the range of 0 to p.s.i.g. and preferably about 50 p.s.i.g. The temperature of the catalyst bed should be in the In view of the fact that under the conditions of low pressure and low recycle gas rates applied in accordance with this invention, the dehydrogenation activity of the platinum metal catalyst is extremely high, so that reaction temperatures may be somewhat lower than used previously. The preferred temperature range is from 875 -950 F.

The naphtha feed is preheated to temperatures in the range of from 900-l050 F., preferably about 975- 1000 F., preparatory to charging the same to the hydroforming reaction zone. Hydrogen or hydrogen process or recycle gas is preheated to 900-l300 F., preferably about 1200 F., preparatory to charging tothe hydro- If desired, the naphtha and hydrogen-rich gas may be heated together in which event the preferred preheat temperature is in the range of from The hydrogen-rich or recycle gas normally contains about 65-90 mol. percent hydrogen with the remainder being light hydrocarbon gases. The exact composition of the recycle gas depends upon the hydroforming reaction conditions and upon the pressure and temperature at which recycle gas is separated from the hydroformate. The amount of recycle gas employed may vary from about 500-5000 and is preferablyabout 1000-3000std. cu. ft. per barrel-of naphtha feed.

In addition to preheating the naphtha feed and. recycle gas, the additional heat load may be supplied to the hydroforming reaction zone by the sensible heat of the regenerated catalyst in fluidized solids operations or by circulating reactor catalyst through a heating zone or by arranging heating coils in the catalyst bed or jacketing the reactor vessel and circulating hot flue gas, mercury, Dowtherm and the like in indirect heat exchange relation to the reaction mixture. The hydroformate and process gases are removed from the reaction zone, passed through suitable catalyst recovery equipment if desired or necessary, and then passed through suitable heat exchanger and condenser equipment, and thence into a gas-liquid Thegaseousproducts are removed from the separator and any excess gas is rejected from the system. The recycle gas may, if desired, be scrubbed to remove hydrogen sulfide and passed through a drier if excessive amounts of water appear therein.

Regeneration of the catalyst is effected as required by burning carbonaceous materials therefrom with oxygencontaining gas at temperatures of 900-l200 F., preferably at 1000-l100 F. The pressure in the regeneration may be the same as during hydroforming or it may, if desired, be lowered to near atmospheric pressure. In burning off the carbonaceous deposits, a certain amount of water is formed by combustion of hydrogen in said deposits. This water is stripped from the regenerated catalyst and passes overhead with the flue gases and is removed from the system. Excess air is used for the regeneration to insure the complete removal of carbon or coke from the catalyst prior to the reactivation of catalyst with chlorine. The regenerated or carbon-free catalyst can advantageously be treated with air at temperatures of 9001l00 F. for from about 1 to 4 hours. The regenerated catalyst is then contacted with chlorine gas or a mixture of chlorine gas and air in order to reactivate the catalyst, restore its chlorine content, and redisperse or break up the large platinum crystallites that form during use of the catalyst.

The chlorine partial pressure may be in the range of from 0.001 to 2 atmospheres, preferably 0.01 to 1 atmosphere. The quantity of chlorine supplied may be in the range of 0.1 to 2.0 wt. percent preferably about 0.5 wt. percent based on the catalyst. The chlorine treatment may be carried out for periods of about seconds to about 1 hour, preferably 1 to 15 minutes. While the chlorine treated catalyst may be subjected to air stripping to remove excess chlorine, it is usually preferred to avoid stripping chlorine from the reactivated catalyst since the chlorine content governs the hydrocracking activity of the catalyst which in turn controls the volatility of the hydroformate. The amount of chlorine, which it is desired to have remaining on the stripped catalyst, is related to the platinum content of the catalyst. With high platinum content catalysts a relatively high chlorine content is desirable and a correspondingly lower chlorine content is desirable for lower platinum contents. In general, the total amount of chlorine (i.e. both chemically combined and adsorbed) remaining on the catalyst when employing a catalyst of 0.6% Pt content may be in the range of about 0.2 to 1.25 wt. percent and is preferably about 0.5 to 1.0 wt. percent.

The hydroformate is withdrawn from the gas-liquid separator and is thereupon subjected to solvent extraction in accordance with the present invention. Suitable solvents for this extraction include such materials as butyrolactone, 2-pyrrolidone, adiponitrile, dimethyl sulfoxide, furfural, phenol, sulfur dioxide and the like.

Of the solvents named, lactones and particularly butyrolactone is the preferred solvent and detailed description will be given for the solvent extraction of the hydroformate with this solvent. It has been found that the lactones and particularly butyrolactone is uniquely effective in selectively removing aromatic constituents from the low-pressure platinum hydroformate of the light virgin naphthas. The precise mechanism by which butyrolactone exhibits these specific and unusual solvent properties is not known at the present time. It seems probable, however, that the particular molecular configuration of this compound combines a critical balance between hydrocarbon solubility and solvent power for the aromatic constituents which has been particularly adapted for the purposes of this invention. It will be understood that minor changes in the extraction procedure obvious to those skilled in this art are or may be required when the selective solvent is changed.

Solvent extractions employing butyrolactone in accordance with this invention may be conducted at temperatures in the broad range of about 50 to 500 F.

However, the selectivity properties of butyrolactone are not critically affected by temperature so that it is generally preferred to operate at moderate temperatures selected to maintain the feed stock in liquid condition.

Thus, in general, a temperature of about to 250 F. is particularly attractive. The extraction can be conducted at any pressure selected from the broad range of about 15 to 750 p.s.i. Again, however, pressure is not particularly critical in the conduct of the extraction making it possible to conduct the process at atmospheric as is normally preferred.

The amount of solvent employed in the practice of this invention varies of course with the particular solvent used and the degree of change required in the properties of the feed stock. In general, however, the amount of solvent to be employed will be from within the range of about 0.5 to 3 volumes of solvent per volume of oil to be treated. For most applications it'is particularly preferred to use about one volume of solvent per volume of oil treated. I

The solvent treating process may be carried out by conventional extraction techniques. Thus, if desired, batch mixing and settling may be employed or continuous and countercurrent treating operations may be employed. In this connection for example, it is particularly preferred to carry out the process'by introducing butyrolactone at an upper portion of a treating tower to flow downwardly countercurrent to the oil to be treated which is introduced near the bottom of the treating tower. Packing elements, perforated plates, or other contacting agents can be employed in such a system. A raffinate phase constituting the treated oil and a minor portion of butyrolactone may be removed'overhead from such a, tower. An extract phase principally constituting butyrolactone and high octane motor fuel constituents will be removed from the bottom of the treating tower.

Solvent may be recovered from the rafiinate and extract phases by conventional techniques. Thus, solvent can be separated from the extract and rafiinate by a simple distillation procedure permitting removal of butyrolactone for recycle to the solvent treating system. Alternatively, and a particular feature of this invention, solvent may be recovered by cooling the extract and rafiinate phases substantially below the extraction temperature. Cooling in this manner results in a change of solvent properties sufiicient to liberate butyrolactone for recycle to the extraction system.

Alternatively, solvent may be recovered by adding water to the extract and rafiinate phases. The addition of water causes the separation of an upper oil layer and a lower layer comprising an aqueous solution of butyrolactone solvent. The lower aqueous solvent layer is withdrawn and may be dehydrated by distillation or other means for recycling to the extraction zone. The hydrocarbon materials separated from the solvent in the extract phase is of high octane number and rich in aromatics and is sent to storage or used for blending or for direct employment as a high octane number motor fuel. The rafiinate phase freed of traces of butyrolactone or other solvent is thereupon recycled in admixture with fresh light naphtha feed to the hydroforming reaction zone for further processing.

The following example is illustrative of the present invention.

Example A light virgin naphtha from West Texas Crude, boiling (5% to in the range of 162 to 191 F. and having an API gravity of 67.9 and a research clear octane number of 66.1, is hydroformed by contacting with a catalyst comprising 0.6 wt. percent platinum deposited on alcoholatc alumina at a temperature of 900 F., a pressure of 50 pounds per square inch, a feed rate of 2.4 weights of naphtha feed per hour per weight of catalyst, and in the presence of 2000 cubic feet of added hydrogen per barrel of feed for a processing period of 20 hours. There is obtained a yield of 87.5 vol. percent of C product having a research octane number of 80.0.

The hydroformed naphtha is extracted in an eleven stage extraction column employing 2 volumes of butyrolactone solvent per volume of hydroformate at a temthe process period is 16 hours instead of 20 hours. The

yield of 80 octane number product is 84.5 vol. percent based on the blended feed. By repeated extraction of the hydroformate and recycle of the raflinates, together with fresh feed, to the hydroforming zone there is obtained an ultimate yield of 67.1 vol. percent of extract based on fresh feed having a research clear octane number of 98.7. When the severity of hydroforming on fresh feed is increased to obtain the same high octane number without extraction, the yield is only 64.0 vol. percent. Furthermore, to obtain this high octane number from this light naphtha feed without extraction very severely limits the throughput of the hydroforming unit since it is necessary to decrease the process period length to about 2 hours and to decrease the feed rate to about 1.2 weights of feed per hour per weight of catalyst.

The foregoing description contains a limited number of embodiments of the present invention. It will be understood, however, that this invention is not limited thereto since numerous variations are possible Without departing from the scope of the following claims.

What is claimed is:

l. A method for producing high octane number, highly aromatic products from hydrocarbon fractions boiling in the range of from about 150 to 200 F. which comprises contacting said fractions in admixture with a hydrogen- .rich gas With a catalyst consisting of a platinum group metal dispersed upon alumina at temperatures of 875- 950 F. and at pressures of about 50 p.s.i.g., maintaining said hydrocarbons in cont-act with catalyst for a period suflicient to produce a C hydroformate having a research clear octane number of about 80, separating the 8 hydroformate from the accompanying normally gaseous materials, subjecting the liquid hydroformate to solvent extraction to obtain an aromatic-rich extract phase and an aromatic-poor rafiinate, and recycling the rafiinate phase to the hydroforming step.

2. A method for producing high octane number, highly aromatic products from hydrocarbon fractions boiling in the range of from about 150 to 200 F. which comprises contacting said fractions in admixture with a hydrogenrich gas with a catalyst consisting of a platinum group metal dispersed upon alumina at temperatures of 875 950 F. and at pressures of about p.s.i.g., maintaining said hydrocarbons in contact with the catalyst for a period sufficient to produce a 0 hydroformate having a research clear octane number of about 80, separating the hydroformate from the accompanying normally gaseous materials, subjecting the liquid hydroformate to solvent extraction with butyrolactone at 50-500 F. to obtain an aromatic-rich extract phase and an aromatic-poor raffinate, and recycling the raffinate phase to the hydroforming step.

3. A method for producing high octane number, highly aromatic products from hydrocarbon fractions boiling in the range of from about 150-200 F. which comprises contacting said fractions in admixture with a hydrogenrich gas with a catalyst consisting of a platinum group metal dispersed upon alumina at temperatures of 875- 950 F. and at pressures of about 50 p.s.i.g., maintaining said hydrocarbons in contact with the catalyst for a period sufficient to produce a (3 hydroformate having a research clear octane number of about 80, separating the hydror'ormate from the accompanying normally gaseous materials, subjecting the liquid hydroformate to solvent extraction with butyrolactone at 250 F. to obtain an aromatic-rich extract phase and an aromatic-poor rafiinate, and recycling the rafiinate phase to the hydroforming step.

References Cited in the file of this patent UNITED STATES PATENTS 2,046,951 Hjerpe et al. July 7, 1936 2,409,695 Laughlin Oct. 22, 1946 2,593,561 Herbst et al. Apr. 22, 1952 2,736,684 Tampoll Feb. 28, 1956 2,740,751 Haensel et al. Apr. 3, 1956 2,767,124 Myers Oct. 16, 1956 2,769,752 Evans Nov. 6, 1956 

1. A METHOD FOR PRODUCING HIGH OCTANE NUMBER, HIGHLY AROMATIC PRODUCTS FROM HYDROCARBON FRACTIONS BOILING IN THE RANGE OF FROM ABOUT 150* TO 200* F. WHICH HYDROGENCONTACTING SAID FRACTIONS IN ADMIXTURE WITH A HYDROGENRICH GAS WITH A CATAALYST CONSISTING OF A PLATINUM GROUP METAL DISPERSED UPON ALUMINA AT TEMPERATURES OF 875* 950* F. AND AT PRESSURES OF ABOUT 50 P.S.I.G., MAINTAINING SAID HYDROCARBONS IN CONTACT WITH CATALYST FOR A PERIOD SUFFICIENT TO PRODUCE A C5+ HYDROFORMATE HAVING A RESEARCH CLEAR OCTANE NUMBER OF ABOUT 80, SEPARATING THE HYDROFORMATE FROM THE ACCOMPANYING NORMALLY GASEOUS MATERIALS, SUBJECTING THE LIQUID HYDROFORMATE TO SOLVENT EXTRACTION TO OBTAIN AN AROMATIC-RICH EXTRACT PHASE AND AN AROMATIC-POOR RAFFINATE, AND RECYCLING THE RAFFINATE PHASE TO THE HYDROFORMING STEP. 